The present invention relates generally to fluid seals, and more particularly, to particular types of oil or like fluid seals, including those which are adapted to work in high pressure environments.
While early fluid seals, particularly for oil, were of a relatively simple design adapted merely to retain grease or the like within a sealed region, development of materials and design, together with requirements of newly developed machines, have resulted in oil seals which are extremely sophisticated and which are able to operate satisfactorily even in very severe service environments. These environments include working with fluids of very low viscosity, operating under high temperature and pressure, and permitting relative movement of varying and complex kinds.
In particular, while many seals are adapted merely to permit relative rotary motion between two sealed parts, and comprise a casing or stiffener portion having a formed annular elastomeric lip bonded thereto, and such seals are usually adapted only to allow relative rotary motion of sealed parts which operate under low pressure. More recently, however, improvements have been made which allow elastomeric lip seals to snugly engage rods or shafts, including those which undergo both reciprocating and rotating motion.
These seals, particularly in specialized applications such as automotive, agricultural, aircraft or like power steering units, for example, or other high pressure hydraulic environments, are adapted to permit both rotary and reciprocating motion, and to achieve a so-called pressure balance both within and without the sealed environments so that increased pressure snugly urges the sealing lip against the sealed member in a more fluid-tight relation, but nevertheless permits desired motion without undue friction or seal damage.
Seals performing in this environment without undue wear often include additional components to prevent the pressure from deforming or extruding the seal along the axis of the shaft or other sealed part. Consequently, it is not uncommon for a seal to include its own primary radially acting lip, and one or more other auxillary lips, but also to include backup rings or washers of a more dimensionally stable material, such as nylon or other synthetic plastic material, and to have these components further backed up or situated by metal rings, clips, washers or the like.
In the development of seals of this kind, great emphasis has been placed on proper pressure balance, prelubrication, lip and spring design, fitting tolerances and the like. However, although great progress has been made, to the point where many applications may be sealed for a period of years without difficulty while permitting operation under pressures from 700 to 1500 psi, and permitting both rotation and reciprocation without substantial loss of fluid, seal failures have begun to be noted in other areas of the seal. According to the present invention, a seal casing or stamping member is made which is adaptable for use with existing molding processes but which is contoured so as to minimize or eliminate undersirable stress concentration where there is a transition between a supported and an unsupported portion of the elastomeric seal.
By way of example, the siffener casing or stamping of a lip seal often comprises an "L" shaped or other contoured annular metal member, usually steel, and usually made by stamping. At the outer diameter of the seal is a mounting flange which may be coated or uncoated steel per se, or may have a rubber or rubberized coating over the exterior thereof, facilitating snug reception in the counterbore of an associated machine member.
The remainder of this casing is used to bond the elastomer and secure it in place, and such seal stiffener or casing normally terminates at its innermost diameter in an edge which is formed as the stamping is formed by a piercing or blanking operation. This area of the inner margin of the casing is sometimes ground or sanded to remove burrs or cut edges, and is then treated for protection against corrosion, as with a phosphate or tin-containing coating, followed by an application of bonding cement. The casing as a whole is then situated with its radially inner margin held within a portion of a compression or injection mold and the seal is formed in such a way as to have its lip portion bonded to the seal during molding.
In the use of such sealing, application of high pressure has been found to cause failures where the pressure tends to displace the unsupported elastomeric seal from the casing in the vicinity of its inside diameter, usually at a sharp edge.
While seals of the type of which the invention is concerned are often not particularly expensive, especially in view of the precision of which they are made, and the high quality materials from which they are made, a seal is often a critical part insofar as it forms a portion of a vital mechanism, often inaccessible, which has a requirement for continued lubrication. Replacing a faulty seal involves effort and inconvenience greatly in excess of that of the cost of the seal per se. Accordingly, there has been a demand for seals which hold out the promise of extended service life in use, and particularly those which are not likely to be rapidly destroyed or damaged by their own working environments.
In view of the need to provide an improved seal for high pressure applications, it is an object of the present invention to provide an improved seal having a contoured casing or stiffener portion.
Another object of the invention is to provide an improved seal which is resistant to failure in high pressure applications.
Yet another object is to provide a seal having a casing which includes an annular bonding bead of increased surface aread and contoured cross-sections, formed in one diameter of the seal casing.
Still another object is to provide a fluid seal for use in high pressure sealing applications, which resists separation or tearing of the elastomer of adjacent the interface between the casing and the elastomer, particularly adjacent a sharp edge thereof.
Yet another object of the invention is to provide a fluid seal unit which provides a marginal bonding portion constructed and arranged so as to cooperate with the bonded elastomeric annular lip seal portion in such a way as to resist failure in use.
A further object of the invention is to provide a casing for a seal unit which includes an annular mounting portion, an intermediate portion and a radially innermost bonding portion, with the bonding portion providing a rounded contour, greatly increased bonding area, and a continuous surface extending from the oil side to at least a part of the air side of the seal casing.
A still further object of the invention is to provide a seal which may be made using existing techniques without measurably increasing the cost of production.
Still another object of the invention is to provide a seal which is conventional in most respects but which is advantageously used in high pressure environments and which may be made without measurable increase in manufacturing costs or requiring the use of additional, exotic materials.
Another object of the invention is to provide a seal which includes a contoured casing and which is adaptable for use in different installations without requiring redesign of the sealed parts.
The seal of the invention achieves these and other inherent and advantages by providing a design which equilizes shearing and other destructive stresses in the finished seal when it is subjected to high pressure application by providing a casing having an inner margin with an increased surface area, and bonding bead having a contoured cross-section, smooth exterior contours, with the bonding surface comprising oil and air side portions, with the entire bonding bead being surrounded by portions of the seal lip body.
The invention also achieves its objects by providing a seal casing which is adapted to receive a bonded lip portion and which may be made without the use of unusual or expensive tools.
The exact manner in which the invention achieves these and other of its objects in practice will be more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example, and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.